photoconjugation and photorelease: an …

PHOTOCONJUGATION AND PHOTORELEASE: AN INVESTIGATION INTO THE

UTILITY OF NAPHTHOQUINONE METHIDE PHOTOCLICK CHEMISTRY

by

JOSHUA ALLEN VALENCIA

(Under the Direction of Jason Locklin)

ABSTRACT

The fast and effective photogeneration of o-naphthoquinone methides (NQM)

from a naphthoquinone methide precursor (NQMP) has been well studied for its use in

protein labelling and the patterning of surfaces. We have developed a method for using

the fast photogeneration of NQM from NQMP derivatives to synthesize an NQMP-

photobase derivative. This neutral molecule is capable of releasing a mild organic base

under a few minutes of ultraviolet irradiation. Additionally, we have investigated a

method of using the fast Diels-Alder reaction of NQM with enamines to conjugate

enamines generated in-situ from aldehydes or ketones to a surface.

INDEX WORDS: COPPER-FREE CLICK CHEMISTRY, PHOTO-CLICK,

NAPHTHOQUINONE METHIDE, PHOTOBASE, DIELS-

ALDER, ENAMINE, FUNCTIONAL SURFACES, CLICK

CHEMISTRY



by


B.S., Kennesaw State University, 2011

A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial

Fulfillment of the Requirements for the Degree

MASTER OF SCIENCE

ATHENS, GEORGIA

2017

© 2017

Joshua Allen Valencia

All Rights Reserved



by


Major Professor: Jason Locklin

Committee: Vladimir V. Popik

Jin Xie

Electronic Version Approved:

Suzanne Barbour

Dean of the Graduate School

The University of Georgia

August 2017

iv

ACKNOWLEDGEMENTS

I would like to thank my advisors Dr. Vladimir Popik and Dr. Jason Locklin for

their advice, guidance, and eternal patience. In addition to teaching me about research,

chemistry, and proper technique, they have each helped teach me about responsibility and

how to properly guide and teach others. I would also like to thank Dr. Jin Xie for his

time, patience, advice, and guidance throughout my graduate career.

Next, I would like to thank my family. Dad, you’ve always been there when I

needed to talk or just to let me know that you were thinking about me. There are so many

times that you’ve called or messaged me at JUST the right time to get me through the

day. Your endless support is something I can always count on, and I don’t know what I’d

do without it. Mom, even though I moved out almost fourteen years ago, home for me

has always been where you and the kids are. You’re such a huge inspiration to me in so

many ways, and I don’t tell you often enough how much I love you. I also want to thank

Mathew, Angela, Stephanie, Patrick, Hannah, Ryan, Summer, Emma, Jackson, Ronnie,

Nathan, and the countless others I’ve been fortunate enough to call my siblings over my

lifetime. Each one of you has brought something special into my life, and each of you has

no idea how much you mean to me. I’m not the best at expressing myself to you guys, but

I love you all so much and would do anything for you.

I’d also like to thank all the lab mates I’ve been fortunate enough to work with

over my graduate school career. Emmanuel, Matt, Chris, Dewey, Masha, Nannan, Kun,

Chris, and Chen of the Popik lab group are incredible assets for any aspiring organic

v

chemist, and I thank you all for the support through the years. Eric, Evan, Joe, Rachelle,

Jenna, Anandi, Jeremy, Jing, Alex, Karson, Deb, Qiaohong, Li, Yutian, Jess, Grant,

Scott, Jess B., Demichael, and Apisata of the Locklin lab have each taught me so much

about characterization, polymerizations, and how to work well with others. A special

thanks to Dr. Chris McNitt and Dr. Dewey Sutton for their incredible knowledge of

organic chemistry that I was lucky enough to take advantage of during our time together.

Dr. Evan White, who has always been supportive and helpful, and who showed me so

many ways to repurpose lab equipment and even household objects to get data. Dr. Joe

Grubbs, whose infectious laughter and great attitude are second only to his incredible

knowledge and his willingness to help others. Dr. Rachelle Benson, who helped me

understand the importance of balancing fun and work by bringing the fun to work. Dr.

Jeremy Yatvin for introducing and welcoming me to the lab and the entire department.

Your friendship in and out of lab got me through a lot of days of struggle. Karson

Brooks, for helping me to keep my sanity throughout my time here. Sometimes I think

the lab would fall apart if you weren’t around. Thanks for keeping us all in line.

Finally, I would like to thank the wonderful friends I’ve made since coming here.

From our first impromptu road trip to late nights, golf games, last-minute casino trips,

and weddings, I couldn’t have done it without you guys and gals being there for me.

Thanks Henry, Majors, Greg, Jeremy, Walter, Karson, Amy, Mary Elizabeth, Jeff, Dave,

Rachelle, Matt, Morgan, Jiana, Josh, Fabian, Charles, Evan, and Justin. You guys are the

best.

vi

TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS ............................................................................................... iv

LIST OF TABLES ........................................................................................................... viii

LIST OF FIGURES ........................................................................................................... ix

LIST OF SCHEMES............................................................................................................x

CHAPTER

1 INTRODUCTION .............................................................................................1

1.1 Click Chemistry .....................................................................................1

1.2 Naphthoquinone Methides .....................................................................5

1.3 Conclusion .............................................................................................6

1.4 References ..............................................................................................7

2 Preparation and Characterization of an NQMP-Based Organic Photobase .....11

2.1 Introduction ..........................................................................................11

2.2 Synthesis of NQMP-Photobase............................................................12 "[Click here and type Subheading]" #

2.3 Properties of NQMP-Photobase ...........................................................13

2.4 Characteristics of NQMP-Photobase Release ......................................13

2.5 Conclusion ...........................................................................................17

2.6 Experimental ........................................................................................17

2.7 References ............................................................................................22

vii

3 Using Surface-Tethered NQMP to Conjugate Aldehydes and Ketones ..........24

3.1 Introduction ..........................................................................................24

3.2 Synthesis of Photoactive Surfaces .......................................................25 "[Click here and type Subheading]" #

3.3 Photoconjugation with Aldehydes and Ketones ..................................28

3.4 Characterization of Surfaces ................................................................29

3.5 Conclusion ...........................................................................................32

3.6 Experimental ........................................................................................33

3.7 References ............................................................................................39

APPENDICES

A 1H and 13C NMR Spectra of Essential Compounds .........................................40

viii

LIST OF TABLES

Page

Table 3.01: Thickness and Contact Angle Measurements for Functionalized Slides. .......30

ix

LIST OF FIGURES

Page

Figure 1.01: General Reaction Scheme of CuAAC .............................................................2

Figure 1.02: Naphthoquinone Methide Photogeneration and Reactions .............................5

Figure 2.01: NQMP-Photobase Release of Propylamine ..................................................12

Figure 2.02: Hydrochloric Acid Neutralization by Propylamine Released from NQMP-

Photobase under Constant Irradiation ....................................................................14

Figure 2.03: Hydrochloric Acid Neutralization by Propylamine Released from NQMP-

Photobase under Pulsed Irradiation .......................................................................16

Figure 3.01: NQMP Reaction with Enamines ...................................................................24

Figure 3.02: Preparation of an Enamine from an Aldehyde ..............................................25

Figure 3.03: In Situ Formation and Conjugation of an Enamine onto NQMP ..................25

Figure 3.04: FTIR Spectra of Silicon Substrates with a) Poly(PFPA), b) Poly(Propargyl

Acrylamide), c) Surface-Tethered Protected NQMP, d) Surface-Tethered NQMP,

e) Surface-Tethered NQMP after Isobutyraldehyde Conjugation .........................31

x

LIST OF SCHEMES

Page

Scheme 2.01: Synthesis of NQMP-Photobase ...................................................................13

Scheme 3.01: Synthesis of Azide-Terminated TEG Linker ..............................................26

Scheme 3.02: Synthesis of Protected Azide-Terminated NQMP ......................................27

Scheme 3.03: Preparation of Protected NQMP-Functionalized Slides .............................28

Scheme 3.04: Deprotection of NQMP-Functionalized Slides ...........................................28

Scheme 3.05: Photoconjugation of Isobutyraldehyde onto NQMP-Functionalized Slides29

1

CHAPTER 1

INTRODUCTION

1.1 Click Chemistry

Background

The term “click” chemistry was coined in 1998 by K. Barry Sharpless to refer to

chemistry that modular, wide in scope, high-yielding, stereospecific, easily purified,

create few or benign byproducts, and use no solvent, or a benign or easily removed

solvent.1

For many applications, whether in the biomedical or material field, the use of volatile

organic solvents, transition metal catalysts, or small molecule byproducts can render an

otherwise robust and versatile chemistry commercially useless. To remedy this, recent

research has turned to various “click” chemistries to solve some of the more taxing

problems in the biomedical and materials field.

While there are many chemistries that have come to be known as “click”

chemistries, some of the most studied and useful examples are the various

cycloadditions.2 These most commonly involve an alkyne or strained alkene, and have

been utilized for everything from drug discovery to protein tagging to surface

modification.2-5

2

Copper(I)-Catalyzed Alkyne-Azide Cycloaddition (CuAAC)

One of the earliest examples of click chemistry is copper(I)-catalyzed alkyne-

azide cycloaddition (CuAAC). This reaction takes place between a terminal alkyne and

an azide to form a 1,2,3-triazole species (Figure 1.1).

Figure 1.01. General Reaction Scheme of CuAAC

These reactions have been carried out with many variations. Studies have been

done involving using a solid support resin for a copper acetylide to react with a terminal

azide to yield a mixture 1,4- and 1,5-disubstituted [1,2,3]-triazoles in good yield under

mild conditions.6 It was also found that this cycloaddition could take place in the

presence of a copper (II) species and a reducing agent such as sodium ascorbate.7 Under

relatively mild conditions, the reaction between an alkyne and an azide would take place

to give predominantly the 1,4-disubstituted [1,2,3]-triazoles in very good yield.7 One of

the biggest drawbacks to this method is its reliance on high catalyst loading and its

limited use outside of terminal alkynes. To address this, studies have recently been done

to address these issues and have found that 1-iodoalkynes are readily accessible internal

alkynes that show an improved reactivity over terminal alkynes, leading to a lowered

reliance on copper catalyst loading.8

3

Strain-Promoted Alkyne-Azide Cycloaddition (SPAAC)

Another method of reducing the reliance on copper catalysts involves the use of a

strained 8-membered cyclic alkyne. Also known as “copper-free click” chemistry,

SPAAC uses the ring strain to increase the reactivity of an internal alkyne to achieve

cycloaddition without the use of a cytotoxic copper catalyst. By using a cyclooctyne, it

was found that the alkyne-azide cycloaddition could take place under mild conditions

without affecting live cell viability.9

Further developments in cyclooctynes has led to the creation of

dibenzocyclooctynes (DIBO)10, difluorinated cyclooctynes (DIFO)11, aza-

dibenzocyclooctynes (ADIBO)12, and oxa-dibenzocyclooctynes (ODIBO)13. Each of

these derivatives shows increased reactivity and kinetics over the original cyclooctyne

moiety when reacting with azides while retaining the same biocompatibility10-13.

Strain-Promoted Alkyne-Nitrone Cycloaddition (SPANC)

Another example of strain-promoted click cycloaddition is strain-promoted

alkyne-nitrone cycloaddition (SPANC). Similar to SPAAC, SPANC does not involve the

use of a copper catalyst to perform the cycloaddition. Instead, SPANC relies on the ring

strain of the alkyne and the increased reactivity of a nitrone over an azide to achieve a

high rate of reaction without the need for a copper catalyst.14 Several studies have found

that it is fairly straightforward to convert various peptides to nitrones, which allow the

use of SPANC to quickly and efficiently label various biological materials.14

Additionally, cyclic nitrones have an even greater reactivity toward strained alkynes,

further increasing the rate.15-17

4

Diels-Alder Cycloaddition

In addition to strained alkyne systems, there are several examples of strained

alkene click chemistry. The most well-known is perhaps Diels-Alder cycloaddition.

Through the use of a diene and an electron-rich dienophile, a [4+2]-cycloaddition can

occur with great speed and without any byproducts or cytotoxic catalysts.

Some of the recent advancements in Diels-Alder cycloaddition include the use of

tetrazines as a diene to increase the rate of the reaction.18-19 These reactions can be used

for protein tagging,18 as well as live cell tagging.19 One advantage that Diels-Alder

cycloaddition has over other forms of click chemistry involves the aqueous environments

in which most biological applications take place. For biological applications, the low

solubility of many of the strained alkynes can limit their usefulness, while the Diels-

Alder reaction with tetrazines not only has increased solubility, but increased rate in

aqueous systems.19

Photoclick

Photochemistry involves using high-energy light to induce a chemical change in a

molecule. The use of light allows a researcher to exert spatial and temporal control over a

reaction. By choosing when and where the reaction takes place, there are many

applications such as in patterning and targeted reaction where photochemistry is the ideal

method. However, photochemistry is not without its drawbacks. The major drawback for

photochemistry in biological systems is the limited penetration depth of most

wavelengths of light. While this limits the usefulness for in-vivo tagging, the control

gained over the reaction is a reasonable tradeoff.

5

There have been several studies that have combined photochemistry with click

chemistry. By utilizing a photolabile cyclopropenone protecting group, ODIBO can be

used in the patterning of surfaces and multifunctional surfaces.3, 13, 20 Additionally, very

reactive Diels-Alder dienes can be prepared photochemically from stable naphthol

derivatives.21

1.2 Naphthoquinone Methides

Naphthoquinone methides (NQMs) are highly reactive molecules under Diels-

Alder and Michael addition conditions. These molecules can be photochemically

generated from naphthol derivatives known as “naphthoquinone methide precursors”

(NQMP) as shown in Figure 1.02.21 Once the NQM is generated, it reacts in a rapid

manner with vinyl ethers and enamines in a Diels-Alder fashion, or in Michael addition

fashion in the presence of thiols.21-22

Figure 1.02. Naphthoquinone Methide Photogeneration and Reactions.

While the Diels-Alder reaction between NQM and enamines and vinyl ethers

proceeds in a non-reversible fashion, the Michael addition between the reactive alkene of

the NQM and a thiol is reversible. This means that the reaction is highly dependent on the

6

concentration of thiol relative to the water in the system.22 Additionally, the NQMP can

be derivatized to release a “payload” of sorts under UV irradiation. By taking advantage

of the reversibility of the reaction and the rapid hydration of NQM back to NQMP, these

derivatives can be used to release a functional molecule or create/remove a pattern from a

surface with temporal and spatial control.21, 23 These reactions allow NQMP to be used as

a versatile caging group for the release of alcohols, thiols, or other groups21, 23, or as a

versatile group for the patterning of surfaces.23-25

1.3 Conclusion

There has been a boom in the past decade of new chemistries that rely on strained

alkynes and alkenes to perform conjugations and surface modifications in a manner that

is fast, simple, clean, and effective. These “click” chemistries show particular promise in

the fields of bioconjugation and materials science. Particularly when these “click”

chemistries are combined with photochemistry, we can begin to achieve a level of control

and functionality far beyond what has been seen in the past.

Of particular interest is the naphthoquinone methide precursor molecule. Through

the rapid generation of the highly reactive naphthoquinone methide moiety under UV

irradiation, we can envision using this molecule for the targeted release of various

functionalities into a system or the targeted capture of various molecules onto a surface

using the rapid Diels-Alder cycloaddition.

7

1.4 References

1. Kolb, H. C.; Finn, M. G.; Sharpless, K. B., Click Chemistry: Diverse Chemical

Function from a Few Good Reactions. Angewandte Chemie International Edition

2001, 40 (11), 2004-2021.

2. Kolb, H. C.; Sharpless, K. B., The growing impact of click chemistry on drug

discovery. Drug Discovery Today 2003, 8 (24), 1128-1137.

3. Arumugam, S.; Popik, V. V., Sequential “Click” – “Photo-Click” Cross-Linker

for Catalyst-Free Ligation of Azide-Tagged Substrates. The Journal of Organic

Chemistry 2014, 79 (6), 2702-2708.

4. Agard, N. J.; Baskin, J. M.; Prescher, J. A.; Lo, A.; Bertozzi, C. R., A

Comparative Study of Bioorthogonal Reactions with Azides. ACS Chemical

Biology 2006, 1 (10), 644-648.

5. Lang, K.; Chin, J. W., Bioorthogonal Reactions for Labeling Proteins. ACS

Chemical Biology 2014, 9 (1), 16-20.

6. Tornøe, C. W.; Christensen, C.; Meldal, M., Peptidotriazoles on Solid Phase:

[1,2,3]-Triazoles by Regiospecific Copper(I)-Catalyzed 1,3-Dipolar

Cycloadditions of Terminal Alkynes to Azides. The Journal of Organic

Chemistry 2002, 67 (9), 3057-3064.

7. Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B., A Stepwise

Huisgen Cycloaddition Process: Copper(I)-Catalyzed Regioselective “Ligation”

of Azides and Terminal Alkynes. Angewandte Chemie International Edition

2002, 41 (14), 2596-2599.

8

8. Hein, J. E.; Tripp, J. C.; Krasnova, L. B.; Sharpless, K. B.; Fokin, V. V.,

Copper(I)-Catalyzed Cycloaddition of Organic Azides and 1-Iodoalkynes.

Angewandte Chemie International Edition 2009, 48 (43), 8018-8021.

9. Agard, N. J.; Prescher, J. A.; Bertozzi, C. R., A Strain-Promoted [3 + 2]

Azide−Alkyne Cycloaddition for Covalent Modification of Biomolecules in

Living Systems. Journal of the American Chemical Society 2004, 126 (46),

15046-15047.

10. Ning, X.; Guo, J.; Wolfert, M. A.; Boons, G.-J., Visualizing Metabolically

Labeled Glycoconjugates of Living Cells by Copper-Free and Fast Huisgen

Cycloadditions. Angewandte Chemie International Edition 2008, 47 (12), 2253-

2255.

11. Codelli, J. A.; Baskin, J. M.; Agard, N. J.; Bertozzi, C. R., Second-Generation

Difluorinated Cyclooctynes for Copper-Free Click Chemistry. Journal of the

American Chemical Society 2008, 130 (34), 11486-11493.

12. Kuzmin, A.; Poloukhtine, A.; Wolfert, M. A.; Popik, V. V., Surface

Functionalization Using Catalyst-Free Azide−Alkyne Cycloaddition.

Bioconjugate Chemistry 2010, 21 (11), 2076-2085.

13. McNitt, C. D.; Popik, V. V., Photochemical generation of oxa-

dibenzocyclooctyne (ODIBO) for metal-free click ligations. Organic &

Biomolecular Chemistry 2012, 10 (41), 8200-8202.

14. Ning, X.; Temming, R. P.; Dommerholt, J.; Guo, J.; Ania, D. B.; Debets, M. F.;

Wolfert, M. A.; Boons, G.-J.; van Delft, F. L., Protein Modification by Strain-

9

Promoted Alkyne–Nitrone Cycloaddition. Angewandte Chemie International

Edition 2010, 49 (17), 3065-3068.

15. McKay, C. S.; Chigrinova, M.; Blake, J. A.; Pezacki, J. P., Kinetics studies of

rapid strain-promoted [3 + 2]-cycloadditions of nitrones with biaryl-aza-

cyclooctynone. Organic & Biomolecular Chemistry 2012, 10 (15), 3066-3070.

16. MacKenzie, D. A.; Sherratt, A. R.; Chigrinova, M.; Cheung, L. L. W.; Pezacki, J.

P., Strain-promoted cycloadditions involving nitrones and alkynes—rapid tunable

reactions for bioorthogonal labeling. Current Opinion in Chemical Biology 2014,

21, 81-88.

17. Friscourt, F.; Fahrni, C. J.; Boons, G.-J., Fluorogenic Strain-Promoted Alkyne–

Diazo Cycloadditions. Chemistry – A European Journal 2015, 21 (40), 13996-

14001.

18. Blackman, M. L.; Royzen, M.; Fox, J. M., Tetrazine Ligation: Fast

Bioconjugation Based on Inverse-Electron-Demand Diels−Alder Reactivity.

Journal of the American Chemical Society 2008, 130 (41), 13518-13519.

19. Devaraj, N. K.; Weissleder, R.; Hilderbrand, S. A., Tetrazine-Based

Cycloadditions: Application to Pretargeted Live Cell Imaging. Bioconjugate

Chemistry 2008, 19 (12), 2297-2299.

20. Brooks, K.; Yatvin, J.; McNitt, C. D.; Reese, R. A.; Jung, C.; Popik, V. V.;

Locklin, J., Multifunctional Surface Manipulation Using Orthogonal Click

Chemistry. Langmuir 2016, 32 (26), 6600-6605.

10

21. Kulikov, A.; Arumugam, S.; Popik, V. V., Photolabile Protection of Alcohols,

Phenols, and Carboxylic Acids with 3-Hydroxy-2-Naphthalenemethanol. The

Journal of Organic Chemistry 2008, 73 (19), 7611-7615.

22. Arumugam, S.; Popik, V. V., Photochemical Generation and the Reactivity of o-

Naphthoquinone Methides in Aqueous Solutions. Journal of the American

Chemical Society 2009, 131 (33), 11892-11899.

23. Arumugam, S.; Popik, V. V., Attach, Remove, or Replace: Reversible Surface

Functionalization Using Thiol–Quinone Methide Photoclick Chemistry. Journal

of the American Chemical Society 2012, 134 (20), 8408-8411.

24. Arumugam, S.; Orski, S. V.; Locklin, J.; Popik, V. V., Photoreactive Polymer

Brushes for High-Density Patterned Surface Derivatization Using a Diels–Alder

Photoclick Reaction. Journal of the American Chemical Society 2012, 134 (1),

179-182.

25. Arumugam, S.; Popik, V. V., Patterned Surface Derivatization Using Diels–Alder


15730-15736.

11

CHAPTER 2

PREPARATION AND CHARACTERIZATION OF AN NQMP-BASED

ORGANIC PHOTOBASE

2.1 Introduction

One of the key strengths of the NQMP photochemistry is the level of spatial and

temporal control that is afforded. There are many situations where a particular chemical

functionality is desired under specific circumstances in a system. One instance where this

may be advantageous involves pH. There are many biological systems that are heavily

dependent on the pH of the surrounding environment.

The adhesive plaques of mussels relies on 3,4-dihydroxyphenylalanine (DOPA)

residues to adhere to iron on ships and rocks.1 This DOPA residue relies on the local pH

of its surroundings to bind or release from the iron. This biological system has been

mimicked to create a hydrogel that can undergo a sol-gel transition based on the pH of

the system.1 To achieve a level of spatial and temporal control over this transition, both a

photoacid generator and a photobase generator are needed.

While there are numerous studies involving the synthesis and characterization of

photoacid generators2-4, there are relatively few organic photobase generators.5 To this

end, we have designed a molecule that will take advantage of the fast photogeneration of

the NQM from NQMP and its derivatives. By derivatizing NQMP with a carbamate

functionality tied into the photocleavage site, we hope to be able to synthesize and

12

characterize a purely organic photobase that can rapidly alter the pH of a system at our

direction (Figure 2.01).

Figure 2.01. NQMP-Photobase Release of Propylamine

2.2 Synthesis of NQMP-Photobase

The target NQMP-photobase 2.04 (Scheme 2.01) was prepared from

commercially available methyl 3-hydroxy-2-naphthoate in four steps. The naphthol was

reacted in a Williamson ether synthesis with sodium hydride (NaH) and chloromethyl

methyl ether in dimethyl formamide to give the protected naphtholic product 2.01. Next,

compound 2.01 was reduced with lithium aluminum hydride (LAH) in tetrahydrofuran to

yield 2.02. Next, compound 2.02 was reacted with propyl isocyanate in dichloromethane

to afford compound 2.03. Finally, compound 2.03 was deprotected with Amberlyst-15

proton exchange resin in 90% methanol in water to give the NQMP-photobase 2.04. In

four steps with a total yield of 53% NQMP-photobase 2.04 can be synthesized in gram-

scale quantities.

13

Scheme 2.01

Reagents and Conditions: a) NaH, chloromethyl methyl ether, DMF, 90%; b) LAH, THF,

94.6%; c) Propyl isocyanate, DMAP, triethylamine, CH2Cl2, 78%; d) Amberlyst 15,

methanol/water 9:1, 80%.

2.3 Properties of NQMP-Photobase

NQMP-photobase 2.04 is an off-white crystalline compound that is shelf stable

for long periods of time if stored away from light. It is stable in water, methanol, and

solutions of the two. Prior to irradiation, the molecule is neutral in a 75% methanol/water

mixture.

2.4 Characteristics of NQMP-Photobase Release

The efficiency and speed of the NQMP-photobase release was measured by pH

probe. NQMP-photobase 2.04 in a tenfold excess was dissolved in a 0.125 mM solution

of hydrochloric acid in a 75% methanol/water mixture. The pH of these solutions was

monitored before, during, and after irradiation to track the release of propylamine by the

neutralization of hydrochloric acid.

14

While under constant irradiation at 310nm, the pH of the solution was checked

every sixty seconds. The solution was initially at pH 4, indicating a fairly acidic solution.

During irradiation, the pH of the solution continually rose, reaching a neutral pH within

ten minutes, and a pH of 8 within twenty minutes. At this point it is assumed that the

released propylamine (pKb = 3.3) is in a buffered equilibrium with the slightly acidic

naphthol on the NQMP (pKa = 9.01) (Figure 2.02).6

Figure 2.02. Hydrochloric Acid Neutralization by Propylamine Released from NQMP-

Photobase under Constant Irradiation.

15

To determine whether the photorelease of the carbamate from the NQMP or the

degradation of the carbamic acid was the rate-limiting factor in the neutralization of acid,

a solution of 1.25 mM NQMP-photobase 2.04 was dissolved in a 0.125 mM solution of

hydrochloric acid in 75% methanol/water. The solution was subjected to one-minute

pulses of irradiation at 310 nm, then the pH was monitored for five minutes. After the

first minute of irradiation, the pH climbed from 4.5 to 5.2. The rate of change of the pH

was found to slow over the five minutes of monitoring after the first minute of irradiation.

After the second minute of irradiation, the pH climbed at a much faster rate, and reached

a pH of 6.6 after five minutes. Unlike the initial irradiation, there was no observable

slowing of the rate of pH change. Subsequent irradiation cycles followed a similar

smooth curve to a final pH of 8.3 after five irradiation cycles (a total of five minutes of

irradiation)(Figure 2.03).

16

Figure 2.03. Hydrochloric Acid Neutralization by Propylamine Released from NQMP-

Photobase under Pulsed Irradiation.

This change in the rate of pH change leads to the conclusion that the degradation

of the carbamic acid is a slower process than the photorelease of the carbamic acid.

Additionally, the steady rate of pH change after two minutes of irradiation suggests that

only two minutes of irradiation is needed to fully convert the NQMP-photobase to

NQMP and carbamic acid. The carbamic acid then degrades into CO2 and propylamine

over the course of twenty minutes.

Further investigation into this phenomenon indicates that this is most likely the

case. Studies have indicated that the degradation of carbamic acids into linear

17

alkylamines takes place on the order of 102-103 M-1s-1.7 The photochemical conversion of

NQMP derivatives into NQM occurs on the order of 104-105 M-1s-1.8 These rates support

the conclusion that the initial release of the carbamic acid from the NQMP-photobase

takes place rapidly under only a few minutes of irradiation, while the degradation of the

released carbamic acid into CO2 and propylamine is a much slower process that takes

several minutes to reach an equilibrium.

2.5 Conclusion

The development of a purely organic photobase using a naphthoquinone methide

photocore was achieved. The NQMP-photobase could be prepared quickly and in high

yields and quantities. The NQMP-photobase is remarkably stable, remaining pure by

NMR after three years of storage on a shelf away from light. The NQMP-photobase

reacts very quickly under 310 nm UV light to release a propyl carbamic acid which

degrades into CO2 and propylamine over a short period of time. The future goals of this

work will be to prepare NQMP-photobase with a synthetic handle that will allow its

integration into materials and surfaces. Additionally, there may be other “payloads” that

can be delivered using this system of photocleavage from an NQMP derivative.

2.6 Experimental

Synthetic Methodology. All syntheses were carried out under an inert atmosphere of

nitrogen using standard Schlenk techniques unless otherwise noted. Unless otherwise

noted, all data was worked up using Origin 9.0.0 SR2 software from OriginLab.

NMR spectroscopy. NMR spectra were recorded using a Varian Mercury 400 NMR

working at 400 MHz for proton spectra and 100 MHz for carbon spectra. Chemical shifts

18

are reported relative to an internal tetramethylsilane standard. The data was worked up

using MNova 10.0.2 software from Mestrelab Research S. L.

UV-Vis measurements. UV-vis spectra were obtained on a Cary 50 Bio UV-vis

spectrophotometer from Varian.

PH measurements. PH measurements were taken on a FiveEasy FE20 pH probe from

Mettler Toledo that was calibrated by two-point calibration using 4.00 and 10.00 buffer

solutions from VWR.

Synthesis of methyl 3-(methoxymethoxy)-2-naphthoate. In a dry round-bottom flask

under positive N2 pressure containing 15 mL dry DMF at 0 °C was added sodium hydride

(NaH) (1.48 g, 37 mmol). To this was added a solution of methyl 3-hydroxy-2-napthoate

(5g, 24.73 mmol) in 10 mL dry DMF dropwise. The solution was allowed to stir under N2

at 0 °C for one hour. While stirring, chloromethyl methyl ether (2.81 mL, 37 mmol) was

added dropwise. The solution was allowed to come to room temperature and stir for five

hours. The solution was then cooled to 0 °C and quenched with water (30 mL) and the

product was extracted with diethyl ether. The organic layer was then washed with water,

brine, and dried over MgSO4. The crude mixture was purified by silica column using

20% ethyl acetate in hexanes mixture. 1H NMR analysis indicated a pure product (5.48 g,

22.25 mmol, 90%). 1H NMR (400 MHz, CDCl3)

Synthesis of (3-(methoxymethoxy)naphthalen-2-yl)methanol. In a dry round-bottom

flask under positive N2 pressure containing 50 mL dry THF at 0 °C was added lithium

aluminum hydride (LAH) (0.927 g, 24.4 mmol). To this was added a solution of methyl

3-(methoxymethoxy)-2-naphthoate (5.47 g, 22.21 mmol) in 20 mL dry THF. The solution

was allowed to come to room temperature and react for three hours while stirring. The

19

solution was then returned to 0 °C and quenched with ethyl acetate (20 mL). The crude

product was filtered through celite with dichloromethane, and the solvent was reduced

under vacuum. The crude product was purified through a silica column with a

dichloromethane/methanol solution (9:1 to 8:2). The solvent was removed under vacuum

to give (3-(methoxymethoxy)naphthalen-2-yl)methanol as a yellow oil (4.583 g, 21.01

mmol, 94.6%). 1H NMR (400 MHz, CDCl3) δ 7.76-7.72 (m, 3H), 7.45-7.42 (t, 1H), 7.40

(s, 1H), 7.38-7.34 (t, 1H), 5.33 (s, 2H), 4.85 (s, 2H), 3.51 (s, 3H).

Synthesis of (3-(methoxymethoxy)naphthalen-2-yl)methyl propylcarbamate. A 15

mL solution of (3-(methoxymethoxy)naphthalen-2-yl)methanol (4.58 g, 21 mmol) in

dichloromethane at 0 °C was added 4-dimethylaminopyridine (0.051 g, 0.42 mmol) and

triethylamine (9 mL, 63 mmol). The solution was allowed to stir for 30 minutes at 0 °C.

To this solution was then added propyl isocyanate (2 mL, 25.2 mmol) dropwise. The

solution was allowed to come to room temperature and stir for four hours. The solution

was then washed with 1M hydrochloric acid, sodium bicarbonate, water, and brine,

passed through celite, and dried under MgSO4 and the solvent was reduced under

vacuum. The crude product mixture was purified through silica with a 75% ethyl

acetate/hexanes solution. The solvent was reduced under vacuum to give (3-

(methoxymethoxy)naphthalen-2-yl)methyl propylcarbamate as a yellow oil (4.985 g,

16.44 mmol, 78 %). 1H NMR (400 MHz, cdcl3) δ 7.79 (s, 1H), 7.75-7.70 (m, 2H), 7.43-

7.39 (m, 2H), 7.35-7.32 (t, 2H), 5.31 (s, 4H), 4.97 (s, 1H), 3.50 (s, 3H), 3.20-3.15 (m,

2H), 1.57-1.48 (m, 2H), 0.94-0.90 (t, 3H). 13C NMR (101 MHz, CDCl3) δ 156.57,

153.00, 134.17, 129.00, 128.46, 127.68, 126.94, 126.80, 126.47, 124.26, 108.85, 94.35,

62.35, 56.17, 42.88, 23.27, 11.27.

20

Synthesis of (3-hydroxynahthalen-2-yl)methyl propylcarbamate. To a round-bottom

flask containing (3-(methoxymethoxy)naphthalen-2-yl)methyl propylcarbamate (4.01 g,

13.22 mmol) in 90% methanol/water (50 mL) was added amberlyst-15 exchange resin

(12 g). The solution was stirred for 48 hours under reflux. The solution was passed

through a paper filter to remove the remaining resin, then extracted with diethyl ether,

washed with water, dried under NaSO4, and the solvent was reduced under vacuum. The

crude product was purified through silica with an ethyl acetate/hexanes solvent system

(60% to 100% EtOAc) and the solvent was removed under vacuum. The remaining

orange semisolid was recrystallized in hot dichloromethane to give (3-

hydroxynaphthalen-2-yl)methyl propylcarbamate as off-white crystals (2.74 g, 10.58

mmol, 80%). 1H NMR (400 MHz, dmso) δ 10.06 (s, 1H), 7.76-7.73 (m, 2H), 7.69-7.67

(d, 1H), 7.40-7.36 (t, 1H), 7.33-7.30 (t, 1H), 7.28-7.25 (t, 1H), 7.18 (s, 1H), 5.16 (s, 2H),

3.02-2.97 (m, 2H), 1.49-1.40 (m, 2H), 0.87-0.84 (t, 3H). 13C NMR (101 MHz, dmso) δ

156.69, 153.86, 134.46, 128.13, 127.86, 127.00, 126.51, 126.08, 123.36, 108.98, 61.59,

42.56, 23.12, 11.66. ESI HRMS: calcd. (M+H+): C15H18NO3 260.1281, found 260.1291.

UV photorelease general sample preparation. To a 0.125 mM solution of hydrochloric

acid in 75% methanol/water (6 mL) in a quartz cell was added (3-hydroxynaphthalen-2-

yl)methyl propylcarbamate (1.9 mg, 0.0075 mmol) to give a 1.25 mM solution of

photobase.

UV photorelease of propylamine. The solution was stirred and irradiated with a hand

lamp equipped with a 300 nm bulb (~1.00 mW/cm2) at a distance of one inch above the

surface of the solution. The pH of the solution was measured prior to the addition of the

photobase, after the addition of the photobase, and every sixty seconds during irradiation.

21

Pulsed UV photorelease of propylamine. The solution was stirred and irradiated in a

UV reactor equipped with eight 300 nm bulbs (~1.00 mW/cm2). The solution was

irradiated for one minute, then removed from the reactor and the pH was monitored for

five minutes before repeating this process for a total of five minutes irradiation. The pH

data was collected prior to irradiation and every fifteen seconds following each

irradiation cycle.

22

2.7 References

1. White, E. M.; Seppala, J. E.; Rushworth, P. M.; Ritchie, B. W.; Sharma, S.;

Locklin, J., Switching the Adhesive State of Catecholic Hydrogels using

Phototitration. Macromolecules 2013, 46 (22), 8882-8887.

2. Shirai, M.; Tsunooka, M., Photoacid and photobase generators: Chemistry and

applications to polymeric materials. Progress in Polymer Science 1996, 21 (1), 1-

45.

3. Li, R.; Nakashima, T.; Kanazawa, R.; Galangau, O.; Kawai, T., Efficient Self-

Contained Photoacid Generator System Based on Photochromic Terarylenes.

Chemistry – A European Journal 2016, 22 (45), 16250-16257.

4. Nakashima, T.; Tsuchie, K.; Kanazawa, R.; Li, R.; Iijima, S.; Galangau, O.;

Nakagawa, H.; Mutoh, K.; Kobayashi, Y.; Abe, J.; Kawai, T., Self-Contained

Photoacid Generator Triggered by Photocyclization of Triangle Terarylene

Backbone. Journal of the American Chemical Society 2015, 137 (22), 7023-7026.

5. Suyama, K.; Shirai, M., Photobase generators: Recent progress and application

trend in polymer systems. Progress in Polymer Science 2009, 34 (2), 194-209.

6. Arumugam, S.; Popik, V. V., Photochemical Generation and the Reactivity of o-

Naphthoquinone Methides in Aqueous Solutions. Journal of the American

Chemical Society 2009, 131 (33), 11892-11899.

7. Caplow, M., Kinetics of carbamate formation and breakdown. Journal of the

American Chemical Society 1968, 90 (24), 6795-6803.

23

8. Kulikov, A.; Arumugam, S.; Popik, V. V., Photolabile Protection of Alcohols,

Phenols, and Carboxylic Acids with 3-Hydroxy-2-Naphthalenemethanol. The

Journal of Organic Chemistry 2008, 73 (19), 7611-7615.

24

CHAPTER 3

USING SURFACE-TETHERED NQMP TO CONJUGATE ALDEHYDES AND

KETONES

3.1 Introduction

One of the most common goals in materials science and surface chemistry is the

fast and versatile conjugation of materials to a surface. NQMP has been shown to be a

powerful tool for conjugating thiols and vinyl ethers to a surface in the past.1-3 However,

the fast Diels-Alder reaction with enamines has not been studied in-depth in the past

(Figure 3.01).4 This is partially due to the relative instability of enamines. They are very

reactive molecules, and their method of preparation is reversible, so they often can

rapidly hydrolize to an inactive state.

Figure 3.01. NQMP Reaction with Enamines.

The standard method of preparing enamines involves reacting an aldehyde or

ketone with an amine (typically a secondary cyclic amine) in the presence of an acid

catalyst (Figure 3.02).5 While this method can give good product yield, the molecule is

not necessarily stable, and preparing and storing large amounts of it may be troublesome.

However, if we were to perform the preparation of an enamine from an aldehyde or

25

ketone in situ while irradiating an NQMP-functionalized surface, we may be able to

“trap” the molecule in its reactive enamine state with our highly reactive NQM. In this

manner, we hope to be able to use the high relative concentration of NQM on a surface to

rapidly and easily conjugate any aldehyde or ketone to a surface using an in situ enamine

generation.

Figure 3.02. Preparation of an Enamine from an Aldehyde.

Figure 3.03. In Situ Formation and Conjugation of an Enamine onto NQMP.

3.2 Synthesis of Photoactive Surfaces

The target azide-terminated triethylene glycol linker was prepared from

commercially available 2-(2-(2-chloroethoxy)ethoxy)ethanol in two steps with a total

yield of 56%. The 2-(2-(2-chloroethoxy)ethoxy)ethanol was reacted with sodium azide in

dimethylformamide to give the azide-terminated triethylene glycol product 3.01. Next,

compound 3.01 was reacted with p-toluenesulfonyl chloride and pyridine in

dichloromethane to give the tosylated triethylene glycol azide product 3.02.

26

Scheme 3.01

Reagents and Conditions: a) NaN3, DMF, 68%; b) p-toluenesulfonyl chloride, pyridine,

CH2Cl2, 82%.

The target azide-terminated protected NQMP derivative was prepared from

commercially available 5-dihydroxy-2-naphthoic acid in four steps with a total yield of

46%. The naphthoic acid was reacted in a Fischer esterification with sulfuric acid

(H2SO4) and methanol to give the methyl ester 3.03. Next, compound 3.03 was reduced

by diisobutylaluminum hydride (DIBAL) in tetrahydrofuran to yield the diol 3.04. Next,

compound 3.04 was reacted with 2,2-dimethyoxypropane and p-toluenesulfonic acid in

acetone to yield the protected diol 3.05. Finally, compound 3.05 was reacted with 3.02

and potassium carbonate in dimethyl formamide to give the azide-termined protected

NQMP derivative 3.06.

27

Scheme 3.02

Reagents and Conditions: a) H2SO4, methanol, 97%; b) DIBAL, THF, 91%; c) 2,2-

dimethoxypropane, p-toluenesulfonic acid, acetone, 95%; d) 3.02, K2CO3, DMF, 55%.

The protected NQMP-derivatized slides were prepared in two steps from

previously prepared grafted-from films of poly(pentafluorophenyl acrylate) (pPFPA) on

quartz, glass, and silicon slides in two steps. The poly(propargyl acrylamide) slides were

prepared by reacting the pPFPA slides with propargyl amine and triethylamine in

dimethylformamide to give the slides functionalized with 3.07. The functionalized slides

3.07 were then reacted with copper (i) bromide, N,N,N’,N”,N”-

pentamethyldiethylenetriamine (PMDETA), and 3.06 in dimethylformamide to give

slides functionalized with 3.08.

28

Scheme 3.03

Reagents and Conditions: a) propargyl amine, triethylamine, DMF; b)CuBr, PMDETA,

3.06, DMF.

The deprotected surface-bound NQMP slides 3.09 were prepared in one step. The

surface-bound protected NQMP slides 3.08 were reacted with hydrochloric acid in

methanol to give the deprotected surface-bound NQMP slides 3.09.

Scheme 3.04

Reagents and Conditions: a) HCl, MeOH.

3.3 Photoconjugation with Aldehydes and Ketones

The conjugation of isobutyraldehyde to the surface-bound NQMP slides was

perfomed in one step. The surface-bound NQMP slides 3.09 were reacted with

29

isobutyraldehyde, morpholine, and p-toluenesulfonic acid in a 50:50 solution of

acetonitrile and water to give conjugate 3.10.

Scheme 3.05

Reagents and Conditions: a) isobutyraldehyde, morpholine, p-toluenesulfonic acid,

310nm hν, acetonitrile/water 1:1.

3.4 Characterization of Surfaces

The functionalized surfaces were characterized by spectroscopic ellipsometry,

drop-shape analysis (DSA), and FTIR. When looking at the change in film thickness and

contact angle (Table 3.01) the initial pPFPA brushes were 44 nm in thickness, and

relatively hydrophobic with a contact angle of 91° as measured by DSA. After

conversion to 3.07, the thickness decreased by 17.5 nm to 26.5 nm. This is expected due

to the much smaller size of the propargyl group compared to the pentafluorophenyl

group. The contact angle also decreased by 22° to 73°, indicating a more hydrophilic

surface. After the reaction with 3.06, the thickness increased by 75.5 nm to 102 nm. This

is due to the much larger size of the tethered protected NQMP compared to the relatively

small propargyl group. The contact angle slightly increased by 10° to 83°, in accordance

with previously published data.1 After deprotection to yield 3.09, the thickness decreased

30

by 19.5 nm to 81.5 nm and the contact angle decreased by 6° to 77°. While these changes

are in the proper direction, they are not as significant as previously reported data.1 This is

likely due to the thickness of the brushes. While the previously reported data was

collected on slides with a thickness of approximately 65 nm, the films used in this study

were 30% thicker at 81 nm.1 This could lead to a drastic change in the degree of

functionalization that is possible under these conditions. After the in-situ conjugation

with isobutyraldehyde, the thickness of the films increased by 6.5 nm to 88 nm, and the

contact angle slightly increased by 2° to 79°. This is expected, as the loss of the alcohol

groups on the NQMP molecule should lead to a more hydrophobic surface.

Table 3.01. Thickness and Contact Angle Measurements for Functionalized Slides.

Brush Thickness Thickness

Change

Contact Angle Contact Angle

Change

Poly(PFPA) 43.97 nm 91°

3.07 26.40 nm -17.57 nm 73° -22°

3.08 101.81 nm +75.41 nm 83° +10°

3.09 81.32 nm -19.5 nm 77° -6°

3.10 87.83 nm +6.51 nm 79° +2°

When examining the FTIR of the substrates (Figure 3.04), we can see the initial

pPFPA brushes have the characteristic C=C aromatic stretches at 1518 cm-1 and C-F

stretches at 1000 cm-1. After reaction with propargylamine, the aromatic peaks and C-F

peaks are lost, and there is the appearance of a C=O amide I stretch at 1656 cm-1, as well

as an sp C-H bend at 3019 cm-1 from the newly added propargyl group. After the

protected NQMP is conjugated to the surface, we see a loss of the sp C-H bend, as well as

a strong peak at 1261 cm-1. While it is not entirely clear, it is possible that this peak

31

corresponds to the C-O stretch from the acetonide protecting group on the NQMP. The

deprotection of the NQMP is also difficult to trace by FTIR. While there is a loss of the

C-O stretch at 1261 cm-1, it cannot be definitively stated whether this corresponds to a

successful deprotection. After the in-situ conjugation with isobutyraldehye, there is

virtually no change in the FTIR of the substrates. The primary difficulty with using FTIR

for this characterization is the thickness of the films. Since the GATR attachment for the

FTIR requires intimate contact with the surface films, very thick films (more than 75 nm)

can be very difficult to analyze using FTIR.

Figure 3.04. FTIR Spectra of Silicon Substrates with a) Poly(PFPA), b) Poly(Propargyl

Acrylamide), c) Surface-Tethered Protected NQMP, d) Surface-Tethered NQMP, e)

Surface-Tethered NQMP after Isobutyraldehyde Conjugation.

32

The glass and quartz substrates that were prepared according to the previously

mentioned procedure were analyzed by UV-Vis spectroscopy to determine the extent of

functionalization with NQMP. Since NQMP has a strong absorbance at 323 nm, it was

expected that this could be used to track the attachment of NQMP to the surface as well

as the extent of conjugation with isobutyraldehyde. Unfortunately, there was little change

in the UV spectrum for either reaction. Again, this is likely due to the thickness of the

films. Since the NQMP moiety is only a fraction of the bulk material on the surface of the

substrates, it is difficult to tease out any small changes in the spectra.

3.5 Conclusion

The development of a new method of conjugating aldehydes and ketones to

surfaces using in-situ enamine formation and trapping via Diels-Alder reaction with

NQM experienced several setbacks. While the protected NQMP could successfully be

attached to the surface, we were unable to determine the success of the deprotection step,

as well as the subsequent conjugation with isobutyraldehyde.

There are several methods that can be used to overcome these difficulties. Thinner

pPFPA films prepared via grafting-to method may make it easier to see the changes in

our substrates by FTIR and UV-Vis. Additionally, other aldehydes or ketones can be used

to determine the success of the conjugation to the deprotected NQMP. An aldehyde with

a long alkyl chain should impart a significant hydrophobicity and increase in contact

angle when it conjugates to the surface. Conversely, a hydrophilic aldehyde or ketone,

such as one based on polyethylene glycol, should show a strong decrease in contact angle

upon conjugation. While the idea of attaching an aldehyde or ketone dye to the surface

33

using this chemistry is an enticing proposition, unfortunately most dyes have a strong

enough absorbance that they may hinder the photoconversion of NQMP to NQM.

If the conjugation of simple aldehydes and ketones onto the NQMP surface can be

performed simply under UV light with mildly acidic conditions, it is not unreasonable to

assume that we can use this method to conjugate several aldehydes or ketones to a

surface using a photomask. With this method, we may be able to have a single surface

that is capable of reacting with a very common functional group, and we can control

when and where these common groups are conjugated to the surface.

3.6 Experimental

Synthetic Methodology. All syntheses were carried out under an inert atmosphere of

nitrogen using standard Schlenk techniques unless otherwise noted. Unless otherwise

noted, all data was worked up using Origin 9.0.0 SR2 software from OriginLab.

NMR spectroscopy. 1H NMR spectra were recorded using a Varian Mercury 300 NMR

working at 300 MHz. 13C NMR spectra were recorded using a [MODEL] 500 NMR

operating at 120 MHz. Chemical shifts are reported relative to an internal

tetramethylsilane standard. The data was worked up using MNova 10.0.2 software from

Mestrelab Research S. L.

Thickness measurements. The film thickness was measured using a J. A. Woolam M-

2000V spectroscopic ellipsometer with a white light source at three angles of incidence

(65°, 70°, and 75°) to the slide normal. The film thickness was fit using a Cauchy model.

Contact angle measurements. The contact angle measurements were obtained using a

Krüss DSA 100 using a 1 μL drop of deionized water. For each measurement, three drops

were recorded and the readings were averaged.

34

UV-Vis measurements. UV-vis spectra were obtained on a Cary 50 Bio UV-vis

spectrophotometer from Varian.

FTIR spectroscopy. Infrared spectra of the surfaces were obtained from a Thermo-

Nicolet Model 6700 spectrometer equipped with a variable angle grazing angle

attenuated total reflection (GATR-ATR) accessory and processed using the Omnic 8.0

software suite.

Synthesis of 2-(2-(2-azidoethoxy)ethoxy)ethanol. In a round-bottom flask containing 2-

(2-(2-chloroethoxy)ethoxy)ethanol (2.27 mL, 15 mmol) in 50 mL dry DMF was sodium

azide (1.463 g, 22.5 mmol) slowly added. The reaction was heated slowly to 100 °C and

stirred for twelve hours. The reaction was cooled to 25 °C, diluted with 100 mL water

and extracted with ethyl acetate. The organic layer was washed with brine, dried with

sodium sulfate, and concentrated under vacuum to give 2-(2-(2-

azidoethoxy)ethoxy)ethanol (1.79 g, 10.2 mmol, 68%) as a colorless oil. 1H NMR (300

MHz, CDCl3) δ 3.73-3.70 (t, 2H), 3.68-3.65 (m, 6H), 3.61-3.58 (t, 2H), 3.39-3.36 (t, 2H),

2.45 (s, 1H).

Synthesis of 2-(2-(2-azidoethoxy)ethoxy)ethyl 4-methylbenzenesulfonate. To a round

bottom flask containing 2-(2-(2-azidoethoxy)ethoxy)ethanol (0.5 g, 2.85 mmol) in 12 mL

dichloromethane was added p-toluenesulfonyl chloride (0.653 g, 3.42 mmol) and

pyridine (0.460 mL, 5.71 mmol). The reaction was allowed to stir at room temperature

for 8 hours. The solution was diluted with 20 mL dichloromethane, washed with water,

washed with 10% copper sulfate solution, dried over magnesium sulfate, and

concentrated under vacuum. The residue was purified through a silica column with 50%

ethyl acetate in hexanes to give 2-(2-(2-azidoethoxy)ethoxy)ethyl 4-

35

methylbenzenesulfonate as a colorless oil (0.770 g, 2.34 mmol, 82%). 1H NMR (300

MHz, CDCl3) δ 7.80-7.77 (d, 2H), 7.35-7.32 (d, 2H), 4.17-4.14 (t, 2H), 3.71-3.67 (t, 2H)

3.65-3.61 (t, 2H), 3.59 (s, 4H), 3.37-3.34 (t, 2H), 2.44 (s, 3H).

Synthesis of methyl 3,5-dihydroxy-2-naphthoate. In a dry round-bottom flask

containing 50 mL methanol was added 5-dihydroxy-2-naphthoic acid (3g, 14.69 mmol).

To this was added concentrated sulfuric acid (0.1 mL, 1.876 mmol). The solution was

allowed to stir under reflux at 67 °C for sixteen hours. The reaction was quenched in 100

mL ice water and extracted with ethyl acetate. The organic layers were dried with

magnesium sulfate and the solvent was removed under vacuum. The remaining dark

yellow solid was dried under vacuum for twelve hours to yield methyl 3,4-dihydroxy-2-

naphthoate (3.12 g, 14.30 mmol, 97%) 1HNMR (300 MHz, CDCl3) δ 10.43 (s, 1H), 8.47

(s, 1H), 7.63 (s, 1H), 7.43-7.40 (d, 1H), 7.19-7.13 (t, 1H), 6.86-6.84 (d, 1H), 5.22 (s, 1H),

3.98, (s, 3H).

Synthesis of 6-(hydroxymethyl)naphthalene-1,7-diol. In a round-bottom flask

containing dry THF at 0 °C was dissolved methyl 3,4-dihydroxy-2-naphthoate (1.09 g, 5

mmol). To this was added dropwise a 1M solution of diisobutyl aluminum hydride (30

mL, 30 mmol) over one hour. The reaction was heated slowly to 45 °C and stirred for

sixteen hours. The reaction was quenched with 50 mL ethyl acetate dropwise at 0 °C. To

remove the remaining aluminum salts, a 300 mg/mL solution of potassium tartrate (150

mL) was added to the flask and the reaction was stirred at 25 °C for fifteen minutes. The

product was extracted with ethyl acetate, washed with water, dried with magnesium

sulfate, and concentrated under vacuum. The residue was recrystallized in chloroform to

yield 6-(hydroxymethyl)naphthalene-1,7-diol as a white solid (0.862 g, 4.5 mmol, 90.6%)

36

1HNMR (300 MHz, DMSO-d6) δ 9.71 (s, 1H), 9.64 (s, 1H), 7.70 (s, 1H), 7.36 (s, 1H),

7.21-7.18 (d, 1H), 7.05-7.00 (t, 1H), 6.72-6.70 (d, 1H), 5.12-5.08 (t, 1H), 4.61 (d, 2H).

Synthesis of 2,2-dimethyl-4H-naphtho[2,3-d][1,3]dioxin-9-ol. In a round-bottom flask

containing 6-(hydroxymethyl)naphthalene-1,7-diol (0.25 g, 1.31 mmol) in 50 mL dry

acetone was added 2,2-dimethoxypropane (0.0.484 mL, 3.94 mmol). To this solution was

added p-toluenesulfonic acid monohydrate (0.011 g, 0.066 mmol) and the reaction was

heated to 50 °C and stirred for five hours. The reaction was quenched with water,

extracted with dichloromethane, washed with water, dried with sodium sulfate, and

concentrated under vacuum to yield 2,2-dimethyl-4H-naphtho[2,3-d][1,3]dioxin-9-ol as a

dark oil (0.302 g, 1.24 mmol, 95%) 1HNMR (300 MHz, CDCl3) δ 7.58 (s, 1H), 7.41 (s,

1H), 7.28-7.25 (d, 1H), 7.14-7.09 (t, 1H), 6.76-6.74 (d, 1H), 5.05 (s, 2H), 1.59, (s, 6H).

Synthesis of 9-(2-(3-(2—azidoethoxy)propoxy)ethoxy)-2,2-dimethyl-4H-naphtho[2,3-

d][1,3]-dioxine. To a round bottom flask containing 2,2-dimethyl-4H-naphtho[2,3-

d][1,3]dioxin-9-ol (0.175 g, 0.76 mmol) and potassium carbonate (0.252 g, 1.824 mmol)

in 3 mL DMF was added a solution of 2-(2-(2-azidoethoxy)ethoxy)ethyl 4-

methylbenzenesulfonate (0.30 g, 0.91 mmol) in 2 mL DMF. The reaction was heated to

60 °C and stirred overnight. The solution was then cooled to room temperature, diluted

with 20 mL diethyl ether, washed with water, dried with magnesium sulfate, and

concentrated under vacuum. The residue was purified through an alumina column with

50% ethyl acetate in hexanes to give 9-(2-(3-(2—azidoethoxy)propoxy)ethoxy)-2,2-

dimethyl-4H-naphtho[2,3-d][1,3]-dioxine as a yellow oil (0.162 g, 0.418 mmol, 55%). 1H

NMR (300 MHz, CDCl3) δ 7.66 (s, 1H), 7.42 (s, 1H), 7.31-7.29 (d, 1H), 7.22-7.17 (t,

37

1H), 6.74-6.72 (d, 1H), 5.06 (s, 2H), 4.29-4.26 (t, 2H), 4.00-3.96 (t, 2H), 3.82-3.79 (t,

2H), 3.72-3.69 (m, 4H), 3.41-3.37 (t, 2H), 1.60 (s, 6H).

Preparation of alkyne functionalized slides. Quartz, glass, and silicon substrates with a

44 nm film of grafted-from poly(pentafluorophenyl acrylate) were reacted overnight into

a solution of 40 mM propargyl amine and 80 mM triethylamine in DMF (2mL). After

reaction the thickness of the film decreased to 29 nm, and infrared spectroscopy indicated

the disappearance of the PFPA peaks and the appearance of two amide peaks. The

contact angle of the slides decreased from 91° to 73°, indicating a slightly more

hydrophilic surface.

Preparation of protected-NQMP-functionalized slides. To a dry, air-free Schlenk flask

containing alkyne-functionalized slides and 16.7 mg CuBr was added a degassed solution

of 13 mM 9-(2-(3-(2—azidoethoxy)propoxy)ethoxy)-2,2-dimethyl-4H-naphtho[2,3-

d][1,3]-dioxine and 24.4 μL PMDETA in DMF. The solution was allowed to stir

overnight at room temperature. The thickness of the films increased to 102 nm, and

infrared spectroscopy indicated the loss of the alkyne peak. The contact angle of the

slides increased to 83°, indicating a slightly more hydrophobic surface.

Deprotection of NQMP-functionalized slides. To a Schlenk flask containing 0.1 M

hydrochloric acid in methanol was placed the protected NQMP-functionalized slides. The

flask was allowed to stir for twelve hours. The thickness of the films decreased to 82 nm.

There was no significant change on the infrared spectrum. The contact angle of the slides

decreased to 77°, indicating a slightly more hydrophilic surface.

Photoconjugation of isobutyraldehyde onto NQMP-functionalized slides. To a

solution of 40 mM isobutyraldehyde, 40 mM morpholine, and 40 mM p-toluenesulfonic

38

acid in 50% acetonitrile in water was placed a glass slide functionalized with NQMP. The

solution was stirred and irradiated under 300 nm light for 20 minutes. The thickness of

the films increased slightly to 88 nm. There was no significant change on the infrared

spectrum. UV-Vis indicated no significant difference in the slide. Contact angle

measurements also indicated no significant difference in the hydrophilicity of the

surfaces.

39

3.7 References

1. Arumugam, S.; Orski, S. V.; Locklin, J.; Popik, V. V., Photoreactive Polymer

Brushes for High-Density Patterned Surface Derivatization Using a Diels–Alder


179-182.

2. Arumugam, S.; Popik, V. V., Attach, Remove, or Replace: Reversible Surface

Functionalization Using Thiol–Quinone Methide Photoclick Chemistry. Journal

of the American Chemical Society 2012, 134 (20), 8408-8411.

3. Arumugam, S.; Popik, V. V., Patterned Surface Derivatization Using Diels–Alder


15730-15736.

4. Arumugam, S.; Popik, V. V., Light-Induced Hetero-Diels−Alder Cycloaddition:

A Facile and Selective Photoclick Reaction. Journal of the American Chemical

Society 2011, 133 (14), 5573-5579.

5. Noack, M.; Göttlich, R., Iodide-Catalysed Cyclization of Unsaturated N-

Chloroamines: A New Way to Synthesise 3-Chloropiperidines. European Journal

of Organic Chemistry 2002, 2002 (18), 3171-3178.

40

APPENDIX A

1H AND 13C NMR SPECTRA OF ESSENTIAL COMPOUNDS

41

Figure A-1. 1HNMR of (3-(methoxymethoxy)naphthalen-2-yl)methyl propylcarbamate.

42

Figure A-2. 13CNMR of (3-(methoxymethoxy)naphthalen-2-yl)methyl propylcarbamate.

43

Figure A-3. 1HNMR of (3-hydroxynaphthalen-2-yl)methyl propylcarbamate.

44

Figure A-4. 13CNMR of (3-hydroxynaphthalen-2-yl)methyl propylcarbamate.

photoconjugation and photorelease: an …

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